1. Field of the Invention
The present invention relates to an ink jet recording head for performing a recording operation by discharging ink onto a recording medium such as a paper or cloth.
2. Related Background Art
In the past, recording apparatuses such as printers, copiers, facsimiles and the like have been designed to record an image comprised of a dot pattern onto a recording material on the basis of image information. Such recording apparatuses are divided into an ink jet type, a wire dot type, a thermal type, a laser beam type and the like on the basis of a recording system; among them, the ink jet type has an ink jet recording head which includes, in an ink liquid path, energy converting means for generating discharge energy utilizing to discharge ink and in which the ink is introduced into the liquid path from a liquid chamber through an ink supply port and the ink is flown as a liquid droplet toward a recording material by the discharge energy applied to the ink from the energy converting means thereby performing a recording operation by adhesion of the liquid droplet.
Among various recording heads, an ink jet recording head for discharging the ink by utilizing thermal energy has been put to practical use since it allows a high density arrangement of ink discharge ports for discharging the ink recording ink to form the ink droplets and it can easily be made compact. Further, in recent years, the number of nozzles included in the ink jet recording head has been increased to satisfy requirement of high speed recording.
By the way, in the recording head of ink jet type, since the ink as fluid is used, due to ink vibration caused by the ink discharging operation, vibration of a meniscus may be disturbed greatly at an opening of the discharge port, which may lead to deterioration of image quality. For example, in the ink jet recording head in which many nozzles are arranged with high density, during the recording operation, since an ink flow amount per unit time is great and an inertia force tending to shift the ink forwardly upon stopping of the discharging becomes also great, positive pressure is applied to the nozzle by such inertia force to protrude the meniscus from the nozzle. In this case, depending upon a circumstance, the ink may be dropped. Alternatively, in the condition that the meniscus is protruded, if a next recording signal is applied, good controlled ink discharging cannot be achieved, but so-called splash ink discharging in which small ink droplets are scattered is generated, with the result that the image quality may be deteriorated.
FIG. 7 is a view showing a pressure vibration wave form generated in an ink flow path by discharge pulses created when a predetermined discharging operation is performed by using a conventional ink jet recording head and FIGS. 8A, 8B and 8C are sectional views each schematically showing a state of a meniscus in the vicinity of an ink discharge port in an A section (before discharging), a B section (during discharging) and a C section (immediately after stoppage of discharging) of FIG. 7.
As shown in FIG. 7, immediately after the stoppage of the discharging, a pressure vibration amplitude a is great to generate positive pressure, and such amplitude will disturb vibration of the meniscus in the next discharging. Explaining in more detail, in the A section of FIG. 7, as shown in FIG. 8A, a stable meniscus M is formed. In this condition, when a heat generating member 53 is operated to perform the discharging operation as in the B section, a good liquid droplet 50 is generated, as shown in FIG. 8B. In the C section immediately after the discharging operation is stopped, due to an inertia force of the ink shifting toward a discharge port 51, pressure in the flow path 52 becomes great to generate positive pressure, with the result that, as shown in FIG. 8C, the meniscus M is formed to be swollen on a discharge port forming face, and, in the worst case, the ink will be dropped from the discharge port 51. Further, if the next recording signal is applied at this timing, splash discharging may occur. In order to solve an inconvenient phenomenon which is caused by the great vibration of the meniscus and which may cause the deterioration of the image quality, there has been proposed a technique in which flow resistance is adjusted by appropriately changing a diameter of a filter provided in an ink supply path extending from an ink tank to the recording head and/or a cross-sectional area of the ink flow path so that the amplitude of the vibration of the meniscus is reduced or stabilized.
As another technique for stabilizing the vibration of the meniscus, as disclosed in Japanese Patent Application Laid-open No. 6-210872, it is known to propose a technique in which a buffer chamber communicating with a common liquid chamber constituting a part of the recording head is provided so that the pressure vibration is absorbed by applying gas (for example, air) into the buffer chamber. This technique is effective as means for suppressing the pressure vibration of the ink in the recording head, and, thus, this technique is adopted in many ink jet recording heads.
In the conventional ink jet recording head in which the ink behavior as shown in FIG. 7 and FIGS. 8A to 8C is caused upon the ink discharging, in a case where the technique for adjusting the flow resistance to stabilize the vibration of the meniscus is adopted, if the flow resistance is set to be great, although the vibration of the meniscus can be improved, the ink supplying into the ink flow path (re-fill) is delayed, with the result that the discharge amount sufficient for the next discharging cannot be obtained, thereby causing poor density. On the other hand, if the flow resistance is set to be small, although the ink supplying can be on time, the amplitude of the vibration of the meniscus cannot be suppressed, with the result that the problem to be improved in nature cannot be solved well. Namely, in the case where the problem regarding the vibration of the meniscus is improved by using the technique for adjusting the flow resistance, the condition setting is limited to the limited range, with the result that a degree of freedom of the design of the ink jet recording head is decreased and unstable factors are included.
To the contrary, in the arrangement in which the buffer chamber is provided in the common liquid chamber (or in the part of the liquid supply path; the term common liquid chamber includes the part of the liquid supply path, hereinafter) within the recording head and the pressure vibration is absorbed by applying the bubbles in the buffer chamber as disclosed in the above mentioned Japanese Patent Application Laid-open No. 6-210872, the sufficient effect for suppressing the vibration of the meniscus can be obtained. However, since the buffer chamber is communicated with the common liquid chamber via the communication portion, in order to prevent the air in the buffer chamber from being exchanged to the ink, it is required that the buffer chamber be made as a closed space except for the communication portion and the liquid be hard to be entered into the buffer chamber through the communication portion by devising the design of the communication portion and the shape of the buffer chamber. Further, regarding a common liquid chamber constituting a part of a very small ink jet recording head, since the buffer chamber must be further added, there is almost no degree of freedom regarding a buffer volume and buffer configuration.
In a case that the ink jet recording head is manufactured, constructional elements must be cleaned to remove dirt or foreign matters therefrom. In a case where the constructional elements of the ink jet recording head having the above-mentioned buffer chamber is cleaned, the interior of the buffer chamber may not be cleaned sufficiently. Further, even if the interior of the buffer chamber can be cleaned, it will take a long time for drying the head after the cleaning. Further, if the cleaning is inadequate, the dirt remaining in the buffer chamber is shifted and is clogged in the ink flow path of the ink jet recording head, thereby causing poor recording.